Related links

gbootroot
- A distribution-creation tool with support for creating UML
root filesystems.

BusyBox
- A Swiss Army knife Linux utility which combines a number of
utilities into one binary. The UML connection is that they use it to
test their stuff and distribute a UML that's been preconfigured for
BusyBox.

There are two Linux on S/390 projects,
IBM's
official port and the
skunkworks
port done by non-IBM people in Germany. UML is essentially the
same idea as IBM's porting its mainframe operating systems to its VM OS.

Minix on Solaris

This is a
port of
Minix to run on Solaris. It is exactly the same idea as UML,
except the guest OS is Minix rather than Linux and the host OS is
Solaris rather than Linux.

Hercules

This is an
S/390
emulator which runs on IA32 and S/390-compatible boxes.
Hercules emulates IBM S/370, S/390 and the new 64-bit zSeries well
enough to run their operating systems, including Linux/390 on IA32
CPUs.

OSKit

From a quick look at
this site
, it seems to be a userspace framework on top of which you can
write on OS. Same basic idea as UML, except more virtual.

NewForge ran an article
about Linux virtual machines which completely failed to
mention UML. The guy who wrote the article was informed of this and
nicely made amends with this
article, which took the form of an interview.

There's also an
article on securitywriters.org about using UML as the basis of
a honeynet.